High charge rate batteries

[plund]

Hello!

I'm trying to figure out battery choice for my system. The plan is to use a 48v 120A solar charger, with batteries to power a load that should be controlled depending on the input power from solar.

The load is able to be adjusted in steps so depending on the input it could either charge the batteries or discharge them together with the solar power. Lets say the steps is 10A, so if the charger give 58A, batteries can help give me 60A on the load. If the charger gives 42A, load is on 40A and 2A to charge batteries.

I'm looking for batteries that can handle a high charge current, since I don't really care about the time it can power the system. The batteries is acting more as a buffer to keep steady current output to the load for rather short moments.

Best case would be something like 2x 50Ah 24V batteries able to charge with 120A but doubt that exist.

Any suggestions on batteries with high C rating or how to design my battery bank?

Thanks!

 

[jgh]

Even the entire 120A would be under 0.5C for a standard 48V pack built from ~300Ah LiFePo4 cells.
If your normal production charge/discharge is 10A, you're not going to be pushing that limit.

Your "short moments" could be an issue; look carefully at how long the inverter/charge-controller takes to respond.

 

[plund]

Thanks for the reply. I mean in case the load is off and batteries need charge, they will take the full 120A and need to be able to handle it. Yeah for sure need to tune it to the solar charger to keep that one happy. Any suggestions on manufacturer for cells like that? I'd prefer 48V 120Ah with 1C but dont know if I can find that.

 

[jgh]

Names like "Gobelpower" and "EVE" come to mind.

Also: clever-enough electronics will be able to limit the battery charge current separately from the to-load current.

 

[SparkyJJO]

How long is "short?" Ideal for LFP in these setups is up to 0.5C continuous, but seems a pretty standard thing is 1C discharge rate is fine for up to 30 seconds. If you have a ~100Ah cells, just limit your charging current to 50A and you'd stay within the 0.5C charge rate to keep things happy.

Or just get some 230Ah (or higher) cells and don't have to worry about it at all as your charge/discharge rates will only tap barely above 0.5C anyway.

 

[plund]

How long is "short?" Ideal for LFP in these setups is up to 0.5C continuous, but seems a pretty standard thing is 1C discharge rate is fine for up to 30 seconds. If you have a ~100Ah cells, just limit your charging current to 50A and you'd stay within the 0.5C charge rate to keep things happy.

Or just get some 230Ah (or higher) cells and don't have to worry about it at all as your charge/discharge rates will only tap barely above 0.5C anyway.

At this moment, no idea how long "short" is. Need to get it up and running and make some experiments to know this.

Names like "Gobelpower" and "EVE" come to mind.

Also: clever-enough electronics will be able to limit the battery charge current separately from the to-load current.

I guess this is what I want to do in the end. I want to be able to have full 120A available for the load, but using smaller batteries and charge them with less current, would be ideal. Would that be something that the solar charger should support, or something done by extra circuitry?

 

[SparkyJJO]

The charger will supply whatever charge current it can provide or is set to provide. Your load will determine whatever your discharge rate is (as long as it isn't above what the BMS and cells can handle). Don't need extra circuitry for any of that.

 

[Mattb4]

At this moment, no idea how long "short" is. Need to get it up and running and make some experiments to know this.



I guess this is what I want to do in the end. I want to be able to have full 120A available for the load, but using smaller batteries and charge them with less current, would be ideal. Would that be something that the solar charger should support, or something done by extra circuitry?

No way to limit charge output from SCC without limiting amperage to the common DC bus that the batteries are on. Some AIO's can function without a battery in circuit. This type might allow you to insert a device before battery to only load the common DC bus at your desired battery max charge rate. Most folks simply install batteries that can handle all the SCC and PV can give them.

 

[Q-Dog]

If you have a charger that puts out 100 amps but a battery that only wants 50 amps to charge, the simple answer is to parallel another battery. Now your battery bank can take 100 amps charging. Another advantage of multiple batteries is, batteries that are not pushed to their limits stay balanced better and last longer.

 

[wpns]

What’s your load (or load profile), and how long do you want the batteries to supply your load in the absence of sunlight?

As other have said, a large enough battery makes all those problems go away.

 

[plund]

I only want the load to be supplied during sunlight. The load is basically a low ohm resistor.

The batteries is not to keep it running 24/7, its to keep stable output throughout sunny hours. The load is multiple parallel stages, so it can be turned on/off according to available sunlight. But every load needs to run at 100% when it's on, why i want the buffer from batteries.

Sure bigger batteries is the easy solution, but space is limited and also don't want to spend more then necessary on batteries as well. Saw something from Victron, DVCC which seem to limit charge current while providing full current to the load.

 

[plund]

No way to limit charge output from SCC without limiting amperage to the common DC bus that the batteries are on. Some AIO's can function without a battery in circuit. This type might allow you to insert a device before battery to only load the common DC bus at your desired battery max charge rate. Most folks simply install batteries that can handle all the SCC and PV can give them.

Well if the controller know it own output, and know the current drawn by the load, it can limit the current right? 100A available, load is at 50A, max charge for batteries is 20A, limit output to 50A+20A. But dont know which controllers supports something like this

 

[SparkyJJO]

I think you'll find it much easier to just properly size the battery. Sure it costs more and takes a bit more space, but how much extra $ will you have in all the fancier controls and equipment and complexity just to try to get away with a smaller battery?

 

[Mattb4]

Well if the controller know it own output, and know the current drawn by the load, it can limit the current right? 100A available, load is at 50A, max charge for batteries is 20A, limit output to 50A+20A. But dont know which controllers supports something like this

No. It limits current based on loading (up to its ability to supply amperage). SCC job is to charge a battery. Loads are loads to it. What limits current to battery is its own internal voltage and amount of other loads that have none.

 

[wpns]

The load is basically a low ohm resistor.

So some kind of heater? If you’re going to be all mysterious the answers you get may be colored by respondents interpretations of your goal.

If you disclose the secret of what you are trying to accomplish someone here may have an idea that could help.

What’s the minimum on-time of these staged heaters?

 

[plund]

So some kind of heater? If you’re going to be all mysterious the answers you get may be colored by respondents interpretations of your goal.

If you disclose the secret of what you are trying to accomplish someone here may have an idea that could help.

What’s the minimum on-time of these staged heaters?

Fair point. Its electrodes for electrolysis. And I have no idea about the minimum on-time at the moment

 

[Mattb4]

Upon some more thought of the subject an additional problem with having a device that limits current to battery off the DC common bus comes to mind. Likely this would isolate or limit the battery from acting as a supply back.

So basically what the OP would like to do is not an available option.

 

[Q-Dog]

I only want the load to be supplied during sunlight. The load is basically a low ohm resistor.

The batteries is not to keep it running 24/7, its to keep stable output throughout sunny hours. The load is multiple parallel stages, so it can be turned on/off according to available sunlight. But every load needs to run at 100% when it's on, why i want the buffer from batteries.

Sure bigger batteries is the easy solution, but space is limited and also don't want to spend more then necessary on batteries as well. Saw something from Victron, DVCC which seem to limit charge current while providing full current to the load.

victron DVCC requires some kind of control device, Venus OS on a raspberry Pi, or a Cerbo or Ekrana, etc. May be cheaper and easier to just install a bigger battery.

 

[plund]

victron DVCC requires some kind of control device, Venus OS on a raspberry Pi, or a Cerbo or Ekrana, etc. May be cheaper and easier to just install a bigger battery.

Sure it adds complexity, but need to control multiple dc dc converters as well so expect something like that would be integrated with that control

 

[plund]

Upon some more thought of the subject an additional problem with having a device that limits current to battery off the DC common bus comes to mind. Likely this would isolate or limit the battery from acting as a supply back.

So basically what the OP would like to do is not an available option.

During normal operation, there will never be too much current available to charge the battery anyways. Guess it could be possible to monitor the load current and the charger current, and if too big of a difference for whatever reason, just limit the output on the charger to not fry the battery. Or what do you think?